Thank you Ken, that is exactly what I was looking for. The local speed limit here is 70, but if that would get me about the same milage with the trans swap as keeping it at 55 it hardly seems worth the cost or hassle for the swap.

Gary, I was wondering the same thing. It seems to me like it is running a little rich. My dad and I are planning on going through it and checking the timing and the adjustment on the carb, just have not had the chance yet. Hopefully we can get the done soon if it is affecting my milage that much. Honestly, when I bought the truck all I was figuring on was about 8 mpg, so 10 to me seemed like a good deal.